/*
 * Copyright (c) 1997-2018 Oracle and/or its affiliates. All rights reserved.
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package cn.taketoday.expression;

/**
 * The interface to a map between EL variables and the EL expressions they are
 * associated with.
 *
 * @since JSP 2.1
 */

public abstract class VariableMapper {

  /**
   * @param variable
   *         The variable name
   *
   * @return the ValueExpression assigned to the variable, null if there is no
   * previous assignment to this variable.
   */
  public abstract ValueExpression resolveVariable(String variable);

  /**
   * Assign a ValueExpression to an EL variable, replacing any previously
   * assignment to the same variable. The assignment for the variable is removed
   * if the expression is <code>null</code>.
   *
   * @param variable
   *         The variable name
   * @param expression
   *         The ValueExpression to be assigned to the variable.
   *
   * @return The previous ValueExpression assigned to this variable, null if there
   * is no previous assignment to this variable.
   */
  public abstract ValueExpression setVariable(String variable, ValueExpression expression);
}
